Coverage issues of satellite based location and positioning services have become extremely popular, largely due to reliability of the Global Navigation Satellite Systems (GNSS) in general and the Global Positioning System (GPS) in particular. Relatively inexpensive but highly accurate GPS receivers and navigation devices have reached a high penetration among car drivers, but GPS based services are very attractive in the public safety and emergency, electrical power distribution, transportation, military and other sectors as well.
Satellite based services often suffer from coverage problems in indoor and closed areas due to the “invisibility” of the satellite signals in such areas. This issue is widely recognized and a number of solution approaches have been proposed and implemented. For instance, GPS repeaters which effectively re-radiate GPS signals in tunnel networks have been reported to extend the coverage area of GPS signals. Unfortunately, the accuracy of positioning services relying on re-radiated GPS signals may become poor due to the nature of how the positioning algorithm works. In simple terms, GPS receivers rely on a generalization of triangulation and the related method of resectioning, in 3 dimensions that are dependent on the time difference of arrivals of GPS signals from different satellite stations.
Global Navigation Satellite System (GNSS) is the standard generic term for satellite navigation systems that enable subscribers to locate their position and acquire other relevant navigational information. The US Global Positioning System (GPS) and the European Galileo positioning system are well known examples of GNSS. GPS is also the only satellite based location method, which is presently operational and is widely adopted for commercial, private and military purposes.
A GPS navigator may either be in the form of a handheld standalone navigator or coupled with a wireless terminal, in a cellular communication system. GPS navigators coupled with user equipments are termed as Assisted GPS (A-GPS), which is tailored to work with a user equipment and thus enables user equipment subscribers to relatively accurately determine their location, time, and even velocity, including direction, in open area environment provided that sufficient number of satellites are visible. By the virtue of assisted GPS, A-GPS enables faster determination of location especially after the cold start. Nonetheless, in both cases the location is determined from the satellite signals.
In a typical cellular system, also referred to as a wireless communications network, the wireless terminals, also known as mobile stations and/or user equipment units (UEs) communicate via a Radio Access Network (RAN) to one or more core networks. The wireless terminals can be mobile stations or user equipments such as mobile telephones also known as “cellular” telephones, and laptops with wireless capability, e.g., mobile termination, and thus can be, for example, portable, pocket, hand-held, computer-included, or car-mounted mobile devices which communicate voice and/or data with radio access network.
The radio access network covers a geographical area which is divided into cell areas, with each cell area being served by a base station, e.g., a Radio Base Station (RBS), which in some networks is also called NodeB, B node or evolved Node B (eNB) and which in this document also is referred to as a base station. A cell is a geographical area where radio coverage is provided by the radio base station equipment at a base station site. Each cell is identified by an identity within the local radio area, which is broadcast in the cell. The base stations communicate over the air interface operating on radio frequencies with the user equipments within range of the base stations.
In some versions of the radio access network, several base stations are typically connected, e.g., by landlines or microwave, to a Radio Network Controller (RNC). The radio network controller, also sometimes termed a Base Station Controller (BSC), supervises and coordinates various activities of the plural base stations connected thereto. The radio network controllers are typically connected to one or more core networks.
The Universal Mobile Telecommunications System (UMTS) is a third generation mobile communication system, which evolved from the Global System for Mobile Communications (GSM), and is intended to provide improved mobile communication services based on Wideband Code Division Multiple Access (WCDMA) access technology. UMTS Terrestrial Radio Access Network (UTRAN) is essentially a radio access network using WCDMA for user equipment units. The Third Generation Partnership Project (3GPP) has undertaken to evolve further the UTRAN and GSM based radio access network technologies. In 3GPP this work regarding the 3GPP Long Term Evolution (LTE) system is ongoing.
GPS based positioning in the 3GPP UTRAN system is already standardized. Similarly, the LTE system provides explicit requirements and support for determining the GPS coordinates of user equipments. User equipments equipped with a GPS navigator and capable of receiving the signals of GPS satellites may determine their own coordinates with a much finer granularity, especially in open areas, than that enabled by path loss, geometry and System Frame Number (SFN) time difference measurements.
Cellular coverage in closed areas, such as city tunnels or underground train tunnels is typically much better than satellite coverage, including GPS coverage. Determining the geographical position using cellular coverage may be based on path loss measurements and reporting that allow the serving base station to calculate the geometry of the served user equipments. Once the geometry is established, base stations may estimate the geographical position by, for instance, using pre-established data bases, obtained during measurement campaigns that associate geometry values with geographical positions, so called spatial coordinates.
A well known specific example is that of the so called location fingerprinting positioning method. It is based on the creation of a radio fingerprint based on path loss or signal strength measurements for each point of a fine coordinate grid that covers the RAN. The fingerprint method may e.g. comprise:                The cell IDs that are detected by the user equipment, in each grid point.        Quantized path loss or signal strength measurements, with regards to multiple radio base stations, performed by the user equipment, in each grid point.        
Whenever a position request arrives at the user equipment, a radio fingerprint is first measured, after which the corresponding grid point is looked up and reported. Determining the user equipment position may also be based on measuring the time difference between the SFNs of the serving cell and different neighboring cells, as in WCDMA systems. In such systems, user equipments may track their positions by measuring SFN-SFN time difference type 2. Since the above mentioned methods rely on cellular coverage, they may easily be employed both in indoor and open area environments.
The main problem of employing GPS repeaters is that the positioning and timing accuracy becomes poor as the indoor or closed area increases. For instance, the GPS positioning error becomes large in long tunnels due to the distorted difference of time arrival of the re-radiated signals as compared to the time arrival difference of the original satellite signals. Another source of inaccuracy is the interference of the original and the repeated GPS signals at the edges and openings of the closed area, e.g. tunnel ends or indoor area lying close to an open area. This is because GPS repeaters use the same frequency for repeating the signal as the original frequencies used by the satellite system.
With the current GPS repeaters, the navigator device always gives the position of the outdoor antenna instead of the real position. This fact and also the increased interference with the original signals result in that the current solutions are not well-suited for navigation in medium and large indoor areas, such as e.g. tunnels, or large urban canyons. Extending the coverage of GPS signals into the GPS-problematic areas while addressing the interference issue is of high importance.
Apart from these technical issues, the installation and operation of GPS repeaters that do not provide the required accuracy are costly. This is problematic, since traditional GPS repeaters typically operate in a business model in which it is difficult to finance the GPS repeater infrastructure. This is because there is no “GPS Operator” and “GPS subscription”, the US government providing the GPS service to the public free of charge, in the sense that would be similar to a subscription based cellular service provisioning.
The widely used mobile phones, even equipped with a GPS navigator, often cannot fully replace advanced GPS navigators implemented as standalone devices, due to, for example, a smaller screen and worse accuracy.